efi_loader: store DT in EFI_RUNTIME_SERVICES_DATA memory

The device tree is needed at runtime. So we have to store it in
EFI_RUNTIME_SERVICES_DATA memory.

The UEFI spec recommends to store all configuration tables in
EFI_RUNTIME_SERVICES_DATA memory.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Alexander Graf <agraf@suse.de>